U.S. patent number 6,996,131 [Application Number 09/538,667] was granted by the patent office on 2006-02-07 for method and apparatus for improving reliability of quick paging of wireless stations.
This patent grant is currently assigned to Nortel Networks Limited. Invention is credited to Khaledul Islam, Arun Munje.
United States Patent |
6,996,131 |
Islam , et al. |
February 7, 2006 |
Method and apparatus for improving reliability of quick paging of
wireless stations
Abstract
Using an initial channel, it is indicated that a message is to
be delivered over at least a further channel. The initial and
further channels are each comprised of at least one time slot. An
initial bit value is assigned to an initial portion of the time
slot of the initial channel. After assigning the initial bit value,
it is determined whether a corresponding portion of the further
channel is available for the message. A further bit value is
assigned to a further portion of the time slot of the initial
channel. The further bit value is indicative of a result of the
determination.
Inventors: |
Islam; Khaledul (Nepean,
CA), Munje; Arun (Nepean, CA) |
Assignee: |
Nortel Networks Limited (St.
Laurent, CA)
|
Family
ID: |
35734296 |
Appl.
No.: |
09/538,667 |
Filed: |
March 30, 2000 |
Current U.S.
Class: |
370/514;
370/320 |
Current CPC
Class: |
H04W
68/00 (20130101); H04W 48/08 (20130101); H04W
74/04 (20130101) |
Current International
Class: |
H04J
3/06 (20060101) |
Field of
Search: |
;370/320,321,322,318,336,335,347,349,441,442,459 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ho; Duc
Assistant Examiner: Tran; Thien D.
Attorney, Agent or Firm: Mintz Levin Cohn Ferris Glovsky
& Popeo
Claims
What is claimed is:
1. A method of indicating, using an initial channel, that a message
is to be delivered over at least a further channel, said initial
and further channels each being comprised of at least one time
slot, said method comprising the steps of: assigning an initial bit
value to an initial portion of said time slot of said initial
channel; determining, after assigning said initial bit value,
whether a corresponding portion of said further channel is
available for said message; and assigning a further bit value to a
further portion of said time slot of said initial channel, said
further bit value being indicative of a result of said
determination.
2. the method of claim 1 wherein said initial bit value always
comprises an indication that said message is present.
3. The method of claim 1 further comprising the step of
determining, before assigning said initial bit value, whether said
corresponding portion of said further channel is available for said
message; and wherein said initial bit value is indicative of a
result of said determination.
4. The method of claim 1 wherein said first portion is within a
first half of said time slot, and said further portion is within a
second half of said time slot.
5. The method of claim 1 further comprising the steps of: further
determining, after assigning said further bit value, whether said
corresponding portion of said further channel is available for said
message; and assigning a still further bit value to a portion at an
end of said time slot of said initial channel, said still further
bit value being indicative of a result of said further
determination.
6. The method of claim 5 wherein said still further bit value
indicates whether at least one of a plurality of further channels
is available for said message.
7. The method of claim 1 wherein said initial channel includes at
least one quick paging channel, said further channel includes at
least one paging channel, said message is a time slotted message,
said initial bit value comprises an initial paging indicator (PI)
bit value, and said further bit value comprises a further pi bit
value.
8. The method of claim 7 wherein said initial pi bit value always
comprises an indication that said message is present.
9. The method of claim 7 further comprising the step of
determining, before assigning said initial PI bit value, whether
said corresponding portion of said paging channel is available for
said message; and wherein said initial PI bit value is indicative
of a result of said determination.
10. The method of claim 7 wherein said time slot is comprised of a
plurality of frames, and said first portion is within a first one
of said plurality of frames and said further portion is within a
third one of said plurality of frames.
11. The method of claim 7 wherein said time slot is comprised of a
plurality of frames, and said first portion is within a second one
of said plurality of frames and said further portion is within a
fourth one of said plurality of frames.
12. The method of claim 7 further comprising the steps of further
determining, after assigning said further PI bit value, whether
said corresponding portion of said paging channel is available for
said message; and assigning at least one reserved bit value to a
portion at an end of said time slot of said quick paging channel,
said reserved bit value being indicative of a result of said
further determination.
13. A method of indicating, using at least one quick paging
channel, that at least one time slotted message is to be delivered
over one of a plurality of paging channels, said quick paging and
said paging channels each being comprised of at least one time
slot, said method comprising the steps of: assigning paging
indicator (PI) bit values to an initial portion of said time slot
of said quick paging channel, said PI bit values being indicative
of whether a corresponding portion of said one of said plurality of
paging channels is available for said message; determining, after
assigning said PI bit values, whether said corresponding portion of
said one of said plurality of paging channels is available for said
message; and assigning at least one reserved bit value to a portion
at an end of said time slot of said quick paging channel, said
reserved bit value being indicative of a result of said
determination.
14. The method of claim 13 further comprising the steps of:
assigning further PI bit values to said initial portion of said
time slot of said quick paging channel, said further PI bit values
being indicative of whether a corresponding portion of at least
another of said plurality of paging channels is available for
another slotted message; further determining, after assigning said
further PI bit values, whether said corresponding portion of said
at least another of said plurality of paging channels is available
for said another message; wherein said reserved bit value is
indicative of a result of said determination and said further
determination.
15. The method of claim 13 further comprising the steps of:
assigning further PI bit values to said initial portion of said
time slot of said quick paging channel, said further PI bit values
being indicative of whether a corresponding portion of at least
another of said plurality of paging channels is available for
another slotted message; further determining, after assigning said
further PI bit values, whether said corresponding portion of said
at least another of said plurality of paging channels is available
for said another message; and further assigning at least another
reserved bit value to said portion at said end of said time slot of
said quick paging channel, said another reserved bit value being
indicative of a result of said further determination.
16. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of at least an odd
numbered one of said plurality of paging channels.
17. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of at least an even
numbered one of said plurality of paging channels.
18. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
first one and a fifth one of said plurality of paging channels.
19. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
second one and a sixth one of said plurality of paging
channels.
20. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
third one and a seventh one of said plurality of paging
channels.
21. The method of claim 13 wherein said reserved bit value is
indicative of a result of said determination of a fourth one of
said plurality of paging channels.
22. A method of indicating, using at least one of a plurality of
quick paging channels, that at least one time slotted message is to
be delivered over one of a plurality of paging channels, said quick
paging and said paging channels each being comprised of at least
one time slot, said method comprising the steps of: assigning
paging indicator (PI) bit values to an initial portion of said time
slot of said one of said plurality of quick paging channels, said
PI bit values being indicative of whether a corresponding portion
of said one of said plurality of paging channels is available for
said message; determining, after assigning said PI bit values,
whether said corresponding portion of said one of said plurality of
paging channels is available for said message; and assigning at
least one reserved bit value to a portion at an end of said time
slot of said one of said plurality of quick paging channels, said
reserved bit value being indicative of a result of said
determination.
23. The method of claim 22 wherein each of said plurality of quick
paging channels is assigned a respective portion of said plurality
of paging channels.
24. The method of claim 23 wherein a first one of a respective
portion of said plurality of paging channels, PCH.sub.first,
assigned to a respective one of said plurality of quick paging
channels, QPCH.sub.q, is determined by the following relation:
.times. ##EQU00005## wherein q has a value from 1 to NUM_QPCH,
NUM_QPCH is a total number of said quick paging channels and
NUM_PCH is a total number of said paging channels.
25. The method of claim 23 wherein a last one of a respective
portion of said plurality of paging channels, PCH.sub.last,
assigned to a respective one of said plurality of quick paging
channels, QPCH.sub.q is determined by the following relation:
.times. ##EQU00006## wherein q has a value from 1 to NUM_QPCH,
NUM_QPCH is a total number of said quick paging channels and
NUM_PCH is a total number of said paging channels.
26. A method of allocating portions of a plurality of paging
channels to respective ones of a plurality of quick paging
channels, said method comprising the steps of: for each of said
plurality of quick paging channels, QPCH.sub.q, wherein q has a
value from 1 to NUM_QPCH, NUM_QPCH is a total number of said quick
paging channels and NUM_PCH is a total number of said paging
channels, the steps of: assigning a first one of a respective
portion of said plurality of paging channels, PCH.sub.First, to
said quick paging channel QPCH.sub.q using the following relation:
.times. ##EQU00007## and assigning a last one of said respective
portion of said plurality of paging channels, PCH.sub.Last, to said
quick paging channel QPCH.sub.q using the following relation:
.times. ##EQU00008##
27. An apparatus for indicating, using an initial channel, that a
message is to be delivered over at least a further channel, said
initial and further channels each being comprised of at least one
time slot, said apparatus comprising: means for assigning an
initial bit value to an initial portion of said time slot of said
initial channel; means for determining, after assigning said
initial bit value, whether a corresponding portion of said further
channel is available for said message; and means for assigning a
further bit value to a further portion of said time slot of said
initial channel, said further bit value being indicative of a
result of said determination.
28. The apparatus of claim 27 wherein said initial bit value always
comprises an indication that said message is present.
29. The apparatus of claim 27 further comprising means for
determining, before assigning said initial bit value, whether said
corresponding portion of said further channel is available for said
message; and wherein said initial bit value is indicative of a
result of said determination.
30. The apparatus of claim 27 wherein said first portion is within
a first half of said time slot, and said further portion is within
a second half of said time slot.
31. The apparatus of claim 27 further comprising: means for further
determining, after assigning said further bit value, whether said
corresponding portion of said further channel is available for said
message; and means for assigning a still further bit value to a
portion at an end of said time slot of said initial channel, said
still further bit value being indicative of a result of said
further determination.
32. The apparatus of claim 31 wherein said still further bit value
indicates whether at least one of a plurality of further channels
is available for said message.
33. The apparatus of claim 27 wherein said initial channel includes
at least one quick paging channel, said further channel includes at
least one paging channel, said message is a time slotted message,
said initial bit value comprises an initial paging indicator (PI)
bit value, and said further bit value comprises a further PI bit
value.
34. The apparatus of claim 33 wherein said initial PI bit value
always comprises an indication that said message is present.
35. The apparatus of claim 33 further comprising means for
determining, before assigning said initial PI bit value, whether
said corresponding portion of said paging channel is available for
said message; and wherein said initial PI bit value is indicative
of a result of said determination.
36. The apparatus of claim 33 wherein said time slot is comprised
of a plurality of frames, and said first portion is within a first
one of said plurality of frames and said further portion is within
a third one of said plurality of frames.
37. The apparatus of claim 33 wherein said time slot is comprised
of a plurality of frames, and said first portion is within a second
one of said plurality of frames and said further portion is within
a fourth one of said plurality of frames.
38. The apparatus of claim 33 further comprising means for further
determining, after assigning said further PI bit value, whether
said corresponding portion of said paging channel is available for
said message; and means for assigning at least one reserved bit
value to a portion at an end of said time slot of said quick paging
channel, said reserved bit value being indicative of a result of
said further determination.
39. An apparatus for indicating, using at least one quick paging
channel, that at least one time slotted message is to be delivered
over one of a plurality of paging channels, said quick paging and
said paging channels each being comprised of at least one time
slot, said apparatus comprising: means for assigning paging
indicator (PI) bit values to an initial portion of said time slot
of said quick paging channel, said PI bit values being indicative
of whether a corresponding portion of said one of said plurality of
paging channels is available for said message; means for
determining, after assigning said PI bit values, whether said
corresponding portion of said one of said plurality of paging
channels is available for said message; and means for assigning at
least one reserved bit value to a portion at an end of said time
slot of said quick paging channel, said reserved bit value being
indicative of a result of said determination.
40. The apparatus of claim 39 further comprising: means for
assigning further PI bit values to said initial portion of said
time slot of said quick paging channel, said further PI bit values
being indicative of whether a corresponding portion of at least
another of said plurality of paging channels is available for
another slotted message; means for further determining, after
assigning said further PI bit values, whether said corresponding
portion of said at least another of said plurality of paging
channels is available for said another message; wherein said
reserved bit value is indicative of a result of said determination
and said further determination.
41. The apparatus of claim 39 further comprising: means for
assigning further PI bit values to said initial portion of said
time slot of said quick paging channel, said further PI bit values
being indicative of whether a corresponding portion of at least
another of said plurality of paging channels is available for
another slotted message; means for further determining, after
assigning said further PI bit values, whether said corresponding
portion of said at least another of said plurality of paging
channels is available for said another message; and means for
further assigning at least another reserved bit value to said
portion at said end of said time slot of said quick paging channel,
said another reserved bit value being indicative of a result of
said further determination.
42. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of at least an odd
numbered one of said plurality of paging channels.
43. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of at least an even
numbered one of said plurality of paging channels.
44. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
first one and a fifth one of said plurality of paging channels.
45. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
second one and a sixth one of said plurality of paging
channels.
46. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of at least one of a
third one and a seventh one of said plurality of paging
channels.
47. The apparatus of claim 39 wherein said reserved bit value is
indicative of a result of said determination of a fourth one of
said plurality of paging channels.
48. An apparatus for indicating, using at least one of a plurality
of quick paging channels, that at least one time slotted message is
to be delivered over one of a plurality of paging channels, said
quick paging and said paging channels each being comprised of at
least one time slot, said apparatus comprising: means for assigning
paging indicator (PI) bit values to an initial portion of said time
slot of said one of said plurality of quick paging channels, said
PI bit values being indicative of whether a corresponding portion
of said one of said plurality of paging channels is available for
said message; means for determining, after assigning said PI bit
values, whether said corresponding portion of said one of said
plurality of paging channels is available for said message; and
means for assigning at least one reserved bit value to a portion at
an end of said time slot of said one of said plurality of quick
paging channels, said reserved bit value being indicative of a
result of said determination.
49. The apparatus of claim 48 wherein each of said plurality of
quick paging channels is assigned a respective portion of said
plurality of paging channels.
50. The apparatus of claim 49 wherein a first one of a respective
portion of said plurality of paging channels, PCH.sub.first,
assigned to a respective one of said plurality of quick paging
channels, QPCH.sub.q, is determined by the following relation:
.times. ##EQU00009## wherein q has a value from 1 to NUM_QPCH,
NUM_QPCH is a total number of said quick paging channels and
NUM_PCH is a total number of said paging channels.
51. The apparatus of claim 49 wherein a last one of a respective
portion of said plurality of paging channels, PCH.sub.last,
assigned to a respective one of said plurality of quick paging
channels, QPCH.sub.q is determined by the following relation:
.times. ##EQU00010## wherein q has a value from 1 to NUM_QPCH,
NUM_QPCH is a total number of said quick paging channels and
NUM_PCH is a total number of said paging channels.
52. An apparatus for allocating portions of a plurality of paging
channels to respective ones of a plurality of quick paging
channels, said apparatus comprising: for each of said plurality of
quick paging channels, QPCH.sub.q, wherein q has a value from 1 to
NUM_QPCH, NUM_QPCH is a total number of said quick paging channels
and NUM_PCH is a total number of said paging channels,: means for
assigning a first one of a respective portion of said plurality of
paging channels, PCH.sub.First, to said quick paging channel
QPCH.sub.q using the following relation: .times. ##EQU00011## and
means for assigning a last one of said respective portion of said
plurality of paging channels, PCH.sub.Last, to said quick paging
channel QPCH.sub.q using the following relation: .times.
##EQU00012##
Description
BACKGROUND OF THE INVENTION
The present invention is directed to wireless communication and,
more particularly, to paging a mobile station.
To conserve battery power, a mobile station, such in a cellular or
personal communications system (PCS) network that employs Code
Division Multiple Access (CDMA), may operate in a slotted mode when
not handling telephone calls and when not receiving information
about the network. While operating in the slotted mode, the CDMA
mobile station periodically monitors only those time slots of a
paging channel (PCH) that are assigned to it to determine whether a
base station is attempting to deliver an incoming call or message
to it. At other times, the mobile station remains in an idle or
standby state. However, the paging channel is shared by many mobile
stations and carries both time slotted and non-time slotted
messages. Therefore, the paging channel may carry information not
intended for the mobile station in its time slot. The mobile
station remains on even when the time slot does not include
information directed to it because the mobile station must monitor
every time slot assigned to it and may be required to monitor up
two time slots in every cycle. Thus, the mobile station consumes
battery power though there is no useful information in the time
slot.
To further conserve power, a quick paging channel (QPCH) has been
added as part of the IS-2000 wireless communication standard. The
quick paging channel is used by the base station to alert an idle
mobile station to activate and receive information carried by the
paging channel starting from the next assigned paging channel time
slot of the idle mobile station. The quick paging channel is
divided into time slots which may include two indicator bits, known
as paging indicator (PI) bits, that are assigned to a respective
mobile station according to a hashing function used by the base
station and the mobile station. The mobile station turns on at the
time it is to receive its assigned PI bits. When both PI bits have
been set to the value ON by the base station, the mobile station
remains active to receive slotted information transmitted over the
paging channel. Alternatively, when one or both of the PI bits have
been set to the value OFF, the mobile station returns to its idle
until the next time that it is to receive PI bits.
However, the quick paging channel PI bits assigned to a specific
mobile station may precede the corresponding paging channel time
slot by as much as 100 ms. This means it is possible for the base
station to turn on the two PI bits assigned to a respective mobile
station, to indicate the presence of a slotted message in the
paging channel, and then be unable to send the message in the
corresponding paging channel time slot. As an example, the base
station may need to transmit a system overhead message, a general
page message or other non-time slotted messages during this time
slot. Alternatively, a slotted message intended for another mobile
station and that began in an earlier paging channel time slot may
run over into the time slot assigned to the current mobile station.
As a further alternative, one or more slotted messages that were
intended for a mobile station that does not support a quick paging
channel may be awaiting delivery because paging channel time slots
in earlier cycles that would ordinarily be assigned to the mobile
station were instead used for mobile stations that were quick
paged. Thus, a mobile station that detected two PI bits that were
set to the value ON and activates to receive a paging channel
message may fail to receive a message, thereby consuming battery
power without receiving a message.
Though algorithms exist for allocating paging channel slots that
may more reliably assure that a mobile station that detects two ON
PI bits actually receives slotted messages on the corresponding
paging channel, such algorithms are typically complex and difficult
to implement in real time. It is therefore desirable that the two
PI bits be assigned in a manner that more reliably indicates that a
slotted message is present on the corresponding paging channel
slot.
SUMMARY OF THE INVENTION
The present invention provides for reliable quick paging of a
mobile station by providing a time lag between the determination of
the value of the first PI bit and the determination of the value of
the second PI bit and by sending subsequent "confirmation" bits.
Some of the bits that are ordinarily specified as "reserved" bits
in the IS-2000 standard are used as the confirmation bits. At the
time each of the second PI bit and the reserved bit is sent, the
base station may determine whether the corresponding paging channel
slot is still available and set the value of the second PI bit and
the values of the reserved bits accordingly.
In accordance with an aspect of the invention, it is indicated,
using an initial channel, that a message is to be delivered over at
least a further channel. The initial and further channels are each
comprised of at least one time slot. An initial bit value is
assigned to an initial portion of the time slot of the initial
channel. After assigning the initial bit value, it is determined
whether a corresponding portion of the further channel is available
for the message. A further bit value is assigned to a further
portion of the time slot of the initial channel. The further bit
value is indicative of a result of the determination.
According to another aspect of the invention, it is indicated,
using at least one quick paging channel, that a time slotted
message is to be delivered over at least one paging channel. The
quick paging and the paging channels are each comprised of at least
one time slot. An initial PI bit value is assigned to an initial
portion of the time slot of the quick paging channel. After
assigning the initial PI bit value, it is determined whether a
corresponding portion of the paging channel is available for the
message. A further PI bit value is assigned to a further portion of
the time slot of the quick paging channel. The further PI bit value
is indicative of a result of the determination.
According to a further aspect of the invention, it is indicated,
using at least one quick paging channel, that at least one time
slotted message is to be delivered over one of a plurality of
paging channels. The quick paging and paging channels are each
comprised of at least one time slot. PI bit values are assigned to
an initial portion of the time slot of the quick paging channel,
the PI bit values being indicative of whether a corresponding
portion of the one of the plurality of paging channels is available
for message. After assigning the PI bit values, it is determined
whether the corresponding portion of the one of the plurality of
paging channels is available for the message. At least one reserved
bit value is assigned to a portion at an end of the time slot of
the quick paging channel, the reserved bit value being indicative
of a result of the determination.
According to yet another aspect of the invention, it is indicated,
using at least one of a plurality of quick paging channels, that at
least one time slotted message is to be delivered over one of a
plurality of paging channels. The quick paging and the paging
channels are each comprised of at least one time slot. PI bit
values are assigned to an initial portion of the time slot of the
one of the plurality of quick paging channels. The PI bit values
are indicative of whether a corresponding portion of the one of the
plurality of paging channels is available for the message. After
assigning the PI bit values, it is determined whether the
corresponding portion of the one of the plurality of paging
channels is available for the message. At least one reserved bit
value is assigned to a portion at an end of the time slot of the
one of the plurality of quick paging channels, the reserved bit
value being indicative of a result of the determination.
According to a still further aspect of the invention, portions of a
plurality of paging channels are allocated to respective ones of a
plurality of quick paging channels. For each of the plurality of
quick paging channels, QPCH.sub.q, wherein q has a value from 1 to
NUM_QPCH, NUM_QPCH is a total number of the quick paging channels
and NUM_PCH is a total number of the paging channels: a first one
of a respective portion of the plurality of paging channels,
PCH.sub.First, is assigned to the quick paging channel QPCH.sub.q
using the following relation: .times. ##EQU00001## and a last one
of the respective portion of the plurality of paging channels,
PCH.sub.Last, is assigned to the quick paging channel QPCH.sub.q
using the following relation: .times. ##EQU00002##
Other features and advantages of the present invention will become
apparent from the following detailed description of the invention
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail in the
following detailed description with reference to the drawings in
which:
FIG. 1 is a diagram showing the relative timing of the quick paging
channel and the paging channel and showing the location of the PI
bits within the quick paging channel.
FIG. 2 is a flow chart illustrating an example of a sequence of
operations for the assignment of the PI bits and reserved bits in
accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a quick paging channel in which the
first PI bit allocated to a respective mobile station is assigned
to a location in the first half of the quick paging channel time
slot and the second PI bit allocated to the mobile station is
assigned to a location in the second half of the time slot. The
second half of the time slot is written at later time, typically 20
40 ms, than the first half so that the values of the bits in the
second half of the time slot may be assigned at a later time than
those of the first half. The value of the second PI bit is not
determined until near the time that the third or fourth frame is
written, rather than at the same time that the value of the first
PI bit is determined. Thus, the base station sends the mobile
station a later and more reliable, indication that a slotted
message is present in the corresponding paging channel time
slot.
Further, one or more bits located at or near the end of the quick
paging channel time slot, which are ordinarily defined as reserved
bits whose values are set to zero in accordance with the first
phase of the IS-2000 standard (protocol revision 6), may have
values that are indicative of the availability of one or more
paging channels that are associated with the respective quick
paging channel. The bits provide a confirmation that the slotted
message is present in the paging channel time slot after the rest
of the quick paging channel time slot is written.
FIG. 1 shows the relative timing of an IS-2000 quick paging channel
and an associated paging channel. Each channel is divided into a
plurality of time slots, and each time slot is further divided into
four frames. Additionally, up to eight reserved bits may be located
after the second and fourth frames of the quick paging channel, and
up to four CCI bits may be located after the reserved bits. The CCI
bits are present only in the first quick paging channel. When a
second and/or a third quick paging channel are used, all of the
bits located after the second and fourth frames of the second and
third quick paging channels are reserved bits.
The first bit of a quick paging channel time slot precedes the
first bit of a corresponding paging channel time slot by a time
interval of typically 100 ms, or the duration of five 20 ms frames,
so that for example, there is a 20 ms interval between the end of
the nth quick paging channel time slot and the first bit of the nth
paging channel time slot.
According to the IS-2000 standard, the first PI bit may be located
in the first frame of the time slot, and the second PI bit may be
thus located in the third frame. Alternatively, the first PI bit is
located in the second frame, and the second PI bit is located in
the fourth frame. The locations of the PI bits within the time slot
are determined by hashing functions based on information specific
to the respective mobile station. Such hashing functions are
defined in the IS-2000 standard. However, a preferred hashing
function for determining the location of the second PI bit is
described in a co-pending U.S. application Ser. No. 09/939,204,
titled "An Improved Hashing Algorithm for a Quick Paging Channel"
and filed by the inventors of the present application on the same
day as the present application, which is incorporated herein by
reference.
FIG. 2 is flow chart illustrating examples of the assignment of PI
bits and reserved bits by a CDMA base station (BTS) according to
the invention. The base station may be any station that
communicates with CDMA mobile stations (MS) but is typically at a
fixed location and is typically part of a cellular system. Further,
the mobile station may be any type of subscriber station used in a
cellular system and includes stations normally intended for use
while in motion or during stops at an unspecified location, such as
automobile or handheld cellular telephones, and includes fixed
subscriber stations.
First, according to an example of the invention referred to as
Option A, the base station determines in a known manner whether any
slotted messages are awaiting transmission to a mobile station that
supports quick paging, as step 200 shows. If no such messages are
present, the mobile station sets the value of the first PI bit to
the value OFF, as step 205 shows. The base station may also
subsequently set the value of the second PI bit to the value OFF,
though this operation is unnecessary because once the mobile
station detects that the first PI bit has the value OFF, it
determines that there are no slotted messages in the corresponding
paging channel slot and may return to an idle state.
If slotted messages are present, the base station determines in a
known manner whether the corresponding paging channel slot is
available for carrying the slotted message, as step 210 shows. As
an example, in FIG. 1, when the nth quick paging channel slot is
assigned to the mobile station and the PI bits are located in the
first and third frames of the slot, the base station may determine
whether the nth paging channel slot is available while assembling
the first frame of paging channel slot n-1.
When the corresponding paging channel slot is available to carry
the slotted message, the base station sets the first PI bit to the
value ON, as step 220 shows. When the corresponding paging channel
slot is not available, the base station sets the first PI bit to
the value OFF, as step 215 shows.
Alternatively, and in the example referred to as Option B, steps
200, 205, 210 and 215 are omitted. Instead, the base station always
sets the first PI bit to the value ON, as step 220 shows. The base
station does not determine whether any slotted messages are
awaiting transmission to the mobile station, thereby reducing the
time required to prepare a transmission from the base station
because the determination of the presence of slotted messages is
not carried out at this time. Also, any slotted messages that
arrive after the first PI bit is set to the value ON, but which
arrive before the value of the second PI bit is determined, may be
included in the paging channel slot that corresponds to the current
quick paging channel slot. Thus, these slotted messages are not
delayed for inclusion in the paging channel slot that corresponds
to the next assigned quick paging channel slot. However, because
the mobile station has to detect the second PI bit, some battery
power may be wasted because of the mobile station must wait until
the second PI bit is detected.
Subsequently, for both Options A and B, the base station waits
until it is at or near the time that the frame containing the
second PI bit is to be written, as shown at step 230, and then
again determines whether the corresponding paging channel slot is
available for carrying the slotted message, as step 240 shows.
When the corresponding paging channel slot is available to carry
the slotted message, the base station sets the second PI bit to the
value ON, as step 250 shows. When the corresponding paging channel
slot is not available, the base station sets the second PI bit to
the value OFF, as step 245 shows. Thus, if the corresponding paging
channel slot becomes unavailable during the 20 40 ms interval
between the time that the first PI bit is set and the time that the
second PI bit is set, the mobile station receives an indication
accordingly from the second PI bit and does not waste battery power
because it does not look for a slotted message in the corresponding
paging channel slot.
After assigning ON values to the two PI bits, the base station
waits until the end of or near the end of the time that the values
of the bits of the final frame of the quick paging channel slot are
assigned, as shown at step 260. Then, the base station may further
verify that the corresponding paging channel time slot is available
for carrying the slotted message and assign values to the reserved
bits located after the final frame accordingly, as step 270 shows.
For example, when the nth quick paging channel slot in FIG. 1 is
assigned to the mobile station, the base station may determine
whether the nth paging channel slot is available while assembling
the final frame of the paging channel slot n-1. When the
corresponding paging channel time slot is still available to carry
the slotted message, the base station sets the corresponding
reserved bit to the value OFF. When the corresponding paging
channel slot is now unavailable, the base station sets the
corresponding reserved bit to the value ON.
To generate the final frame of a quick paging channel time slot,
the base station uses two frame drivers whose outputs are summed to
form the final frame. Ordinarily, the value of each bit of a frame
must be known at the time the frame is formed, including the value
of the reserved bits. The invention, however, determines the
availability of the paging channels, and thereby assigns values to
the reserved bits of the final frame, at a time later than the
final frame is ordinarily defined. To allow for the later
definition of the reserved bits, the invention uses a first driver
to first define a final frame having all reserved bits equal to
zero. Thereafter, typically 18.75 msec after the first driver has
defined the frame, the second driver defines a frame whose the
non-reserved bits are equal to zero and whose reserved bits have
value dependent upon the presence of slotted messages in the
respective paging channels, as described above. The frames supplied
by each of the drivers are then summed to form the final quick
paging channel frame that is transmitted by the base station.
The assignment of the reserved bits and their values are determined
by the number of quick paging channels used by the base station,
NUM_QPCH, the number of paging channels used by the base station,
NUM_PCH, and whether the messages are being transmitted at a full
rate, typically 9600 bps, or at a half rate having half the number
of bits in a frame as are in a full rate frame, typically 4800 bps.
The IS-2000 wireless communication standard allows a base station
to transmit over up to seven paging channels and over up to three
quick paging channels. Ordinarily, the paging channels are not
assigned to a respective quick paging channel. Instead, the quick
paging channel assigned to a respective mobile station, the
location of the PI bits assigned to the mobile station and the
paging channel assigned to the mobile station are determined by
hashing functions which base the determination on information
specific to the mobile station, such as its telephone number.
However, in accordance with the invention, a closed-form formula
defines how each of the paging channels is assigned to a respective
one of the quick paging channels. For a given mobile station, the
paging channel and the associated quick paging channels, as well as
the location of the PI bits assigned to the respective mobile
station, are determined by hashing functions. The hashing functions
are defined in the IS-2000 standard, though a preferred hashing
function for determining the location of the second PI bit is
disclosed in the above-mentioned co-pending U.S. application Ser.
No. 09/539,204.
The paging channels are assigned to the respective quick paging
channels as follows:
(1) Each of the quick paging channels (QPCH.sub.1, . . . ,
QPCH.sub.NUM.sub.--.sub.QPCH) is assigned a respective portion of
the paging channels (PCH.sub.1, . . . ,
PCH.sub.NUM.sub.--.sub.PCH).
(2) The first one of the portion of paging channels, known as
PCH.sub.First, assigned to a quick paging channel QPCH.sub.q, where
q has a value from 1 to NUM_QPCH, is determined by the following
relation: .times. ##EQU00003## where the floor function y=.left
brkt-bot.x.right brkt-bot. is defined such that y is the greatest
integer having a value less than or equal to x.
(3) The last one of the portion of paging channels, known as
PCH.sub.Last, assigned to the quick paging channel QPCH.sub.q is
determined by the following relation: .times. ##EQU00004## where
the ceiling function y=.left brkt-top.x.right brkt-bot. is defined
such that y is the smallest integer having a value greater than or
equal to x.
As an example, when there are five paging channels (PCH.sub.1,
PCH.sub.2, . . . , PCH.sub.5) and two quick paging channels
(QPCH.sub.1, QPCH.sub.2), then NUM_PCH=5 and NUM_QPCH=2. Using the
above two relations, the first and last paging channels assigned to
each of the quick paging channels are determined. The first one of
the portion of paging channels, PCH.sub.First, assigned to the
first quick paging channel QPCH.sub.1 is determined from the first
of the above relations, i.e. First=.left brkt-bot.0.right
brkt-bot.+1=1, so that the first paging channel assigned to
QPCH.sub.1 is PCH.sub.1. The last one of the portion of paging
channels, PCH.sub.Last, assigned to the first quick paging channel
QPCH.sub.1 is determined from the second one of the above
relations, i.e. Last=.left brkt-top.2.5.right brkt-bot.=3, so that
the last paging channel assigned to QPCH.sub.1 is PCH.sub.3. Thus,
the first, second and third paging channels are assigned to the
first quick paging channel. Similarly, the first one of the portion
of paging channels, PCH.sub.First, assigned to the second quick
paging channel QPCH.sub.2 is determined from the first one of the
above relations, i.e. First=.left brkt-bot.2.5.right
brkt-bot.+1=2+1=3, so that the first paging channel assigned to
QPCH.sub.2 is PCH.sub.3. The last one of the portion of paging
channels, PCH.sub.Last, assigned to the second quick paging channel
QPCH.sub.2 is determined from the second one of the above
relations, i.e. Last=.left brkt-top.5.right brkt-bot.=5, so that
the last paging channel assigned to QPCH.sub.2 is PCH.sub.5. Thus,
the third paging channel is divided between the two quick paging
channels, and the fourth and fifth of the five paging channels are
assigned solely to the second quick paging channel.
The paging channels assigned to a respective quick paging channel
are represented by the reserved bits of that quick paging channel
in the following manner:
(1) When only one quick paging channel is used, i.e. when
NUM_QPCH=1, up to seven paging channels may be assigned to the
quick paging channel. For half rate transmission, there are two
reserved bits in the final frame of each time slot. The first
reserved bit of the final frame is allocated to the odd-numbered
paging channels, namely the first paging channel and, when present,
the third, fifth and seventh paging channels. The second bit of the
final frame is allocated to the even-numbered paging channels,
namely the second, fourth and sixth paging channels, when one or
more of these channels is present. When neither the first, third,
fifth nor seventh paging channel carries a slotted message, the
first reserved bit has the value ON. Alternatively, when one or
more of the first, third, fifth and seventh paging channels carries
slotted messages, the first reserved bit has the value OFF.
Similarly, when neither the second, fourth nor sixth paging channel
carries a slotted message, the second reserved bit has the value
ON, and when one or more of the these paging channels carries
slotted messages, the second reserved bit has the value OFF.
For full rate transmission, there are at least four reserved bits
in the final frame of each time slot. The first bit of the final
frame is allocated to the first paging channel and, when present,
the fifth paging channel. The second bit is allocated to the second
and sixth paging channels, when one or more of these channels is
present. The third bit is allocated to the third and seventh paging
channels, when one or more of the channels is present, and the
fourth bit is allocated to fourth paging channel, when present.
When neither the first nor fifth paging channel carries a slotted
message, the first reserved bit has the value ON, and when one or
more of these paging channels carries slotted messages, the first
reserved bit has the value OFF. When neither the second nor sixth
paging channel carries a slotted message, the second reserved bit
has the value ON, and when one or more of the these paging channels
carries slotted messages, the second reserved bit has the value
OFF. When the neither the third nor seventh paging channel carries
a slotted message, the third reserved bit has the value ON, and
when one or more of the these paging channels carries slotted
messages, the third reserved bit has the value OFF. When the fourth
paging channel does not carry a slotted message, the fourth
reserved bit has the value ON, and when the these paging channel
carries slotted messages, the fourth reserved bit has the value
OFF.
(2) When there are two or three quick paging channels, i.e. when
NUM_QPCH.gtoreq.2, up to four paging channels may be assigned to a
respective quick paging channel. For half rate transmission, two
reserved bits in the final frame of each time slot are assigned to
the first quick paging channel, and four additional reserved bits
are assigned to the second quick paging channel or, when a third
quick paging channel is present, are divided between the second and
third quick paging channels. The paging channels assigned to the
first quick paging channel are represented by the reserved bits of
the first quick paging channel in the manner described above.
Because a total of, at most, four paging channels are assigned
between the second and third quick paging channels, each of the
four reserved bits assigned to these two quick paging channels is
allocated to a respective paging channel in the order that the
paging channels are assigned to the quick paging channels. Thus,
the first of the four bits is allocated to the first paging channel
that is assigned to the second quick paging channel, namely paging
channel PCH.sub.2,First. The second bit is allocated to the next
paging channel that is assigned to the second quick paging channel,
which may be paging channel PCH.sub.2,Last, or when only one paging
channel is assigned to the second quick paging channel, the second
bit is allocated to the first paging channel that is assigned to
the third quick paging channel, namely paging channel
PCH.sub.3,First. The remainder of the four bits are similarly
assigned.
For full rate transmission, four reserved bits in the final frame
of each time slot are assigned to the first quick paging channel,
and eight additional reserved bits are assigned to the second quick
paging channel or, when a third quick paging channel is present,
are divided between the second and third quick paging channels. The
paging channels assigned to the first quick paging channel are
represented by the reserved bits of the first quick paging channel
in the manner described above. Because a total of, at most, four
paging channels are assigned between the second and third quick
paging channels, only four of the eight reserved bits are used and
each of the four bits is allocated to a respective paging channel
in the order that the paging channels are assigned to the quick
paging channels, as described above.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses may become apparent to those skilled
in the art. It is preferred, therefore, that the present invention
be limited not by this specific disclosure herein, but only by the
appended claims.
* * * * *